Gas-operation is a system used to provide energy to operate auto-loading firearms. In gas-operation, a portion of high pressure gas from the cartridge being fired is used to power a mechanism to extract the spent case and chamber a new cartridge. Energy from the gas is harnessed through either a port in the barrel or trap at the muzzle. This high-pressure gas impinges on a movable surface such as a piston head to provide motion for unlocking the action, extracting and ejecting the spent case, cocking the hammer or striker, chambering a fresh cartridge, and locking the action.
Most current gas systems employ some type of piston. The face of the piston is acted upon by gas from the combustion of the propellant from the barrel of the firearm. Early methods such as Browning's ‘flapper’ prototype, the Bang rifle, and Garand rifle used relatively low-pressure gas from at or near the muzzle, where the bullet exits the barrel. This, combined with more massive operating parts, reduced the strain on the mechanism. To simplify and lighten the firearm, gas from nearer the chamber needed to be used. This gas is of extremely high pressure and has sufficient force to destroy a firearm unless it is regulated somehow. Several methods are employed to regulate the energy. The M1 carbine incorporates a very short piston, or “tappet”. This movement is closely restricted by a shoulder recess. Excess gas is then vented back into the bore. The M14 rifle and 60 GPMG use the White expansion and cutoff system to stop (cut off) gas from entering the cylinder once the piston has traveled a short distance. Most systems, however, vent excess gas into the atmosphere through slots, holes, or ports.
With a long-stroke system, the piston is mechanically fixed to the bolt group and moves through the entire operating cycle. This system is used in weapons such as the Bren light machine gun, AK-47, Tavor, M249 Squad Automatic Weapon, FN MAG, M1 Garand, and various semi-automatic shotguns, for example. The primary advantage of the long-stroke system, beyond design simplicity and robustness, is that the mass of the piston rod adds to the momentum of the bolt carrier enabling more positive extraction, ejection, chambering, and locking. Also, as the gas is not directed back into the chamber, the weapon stays cleaner longer thus reducing the likelihood of a malfunction.
Simplified section views of a typical gas-operation system in use are depicted in FIGS. 1A-1E. A typical long-stroke gas-operation system 100 of a firearm may comprise a barrel 105 having a gas port 110 located distally down the barrel 105, well away from the chamber 170. The gas port 110 vents part of the pressurized gas 165 resulting from the firing of gunpowder 155 causing a bullet or other projectile(s) 150 (herein collectively, “bullet 150”) to travel down the barrel 105 from a proximal end near the chamber 170 to a distal end where the bullet exits the barrel 105 through a muzzle (not shown). The gas port 110 typically vents a small portion of the pressurized gas 165 into an adjacent cylinder 115 just beyond a piston 120 located in the cylinder 115, as depicted in FIGS. 1B-1D. The piston 120 is typically connected by a piston rod or operation rod 125 to a bolt carrier 130, those parts together comprising a carrier assembly that typically slides in the opposite direction of the bullet 150 (i.e., rearward, or to the right in the Figures) when the pressurized gas 165 travels down the barrel 105 behind the bullet 150, through the gas port 110, into the cylinder 115, and impinges on the face of the piston 120, as depicted in FIGS. 1B-1D. The momentum of the rearward travel of the bolt carrier assembly typically causes the bolt carrier 130 to unlock a locking block 145 that locks the bolt 140 to the chamber 170 (i.e., unlocks the “action”), and then the bolt carrier 130 pushes the bolt 140 backwards (to the right in the Figures) away from the chamber 170, while expelling the spent casing 160 and introducing a new cartridge with bullet 150 into the chamber 170, as depicted in FIG. 1E. The rearward travel of the carrier assembly is typically increasingly resisted by a spring 135, which then urges the carrier assembly to travel back in the forward direction (to the left in the Figures, FIG. IF), re-locking the bolt 140 to the chamber 170, whereupon the firearm returns to the position shown in FIG. 1A, ready to fire again.
One disadvantage of this type of system 100 is that, due to the significant mass of moving parts, a significant amount of high-pressure gas 165 is required to operate the system 100. In order to transmit the required volume of high-pressure gas 165 to the piston 120, manufacturers utilize various numbers of gas ports 110 of different sizes, typically located near or distally (to the left in the Figures) of the resting position of the piston 120 to allow the high-pressure gas 165 to flow backward (to the right in the Figures) against the face of the piston 120. There are some key limitations to this type of system 100. First, these small ports 110 are prone to clogging due to debris created when a round or bullet 150 is fired. Clogged ports 110 can cause the firearm to cease functioning as intended.
Second, the size and/or number of ports 110 can directly affect the types of loads that can be used. If the ports 110 are small or there are few of them it is more difficult for high-pressure gas 165 to be redirected to the piston 120. This results in the firearm requiring heavy loads (high-powered cartridges) in order for the gas-operation system 100 of the firearm to cycle. Alternatively, if ports 110 are larger or more numerous then gas 165 is more easily redirected, which can allow the firearm to cycle lighter loads (lower-powered cartridges). However, where large ports 110 are used, heavy loads may cause excessive wear on the firearm due to exposing the face of the piston 120 to an excessive volume of high-pressure gas 165 directly from the interior of the barrel 105.
A third limitation of typical systems 100 is the distal location of the ports 110. By placing the ports 110 in a distal portion of the barrel 150 (distally from the firing chamber 170) adjacent or beyond the resting position of the piston 120, the pressure of the high pressure gas 165 available at the ports 110 is greatly reduced and is widely variable depending on the power of the cartridge 150. Thus, present systems 100 provide inefficient and inconsistent capturing and transmission of high-pressure gas 165.